Multicore fiber, optical fiber cable, and optical connector

ABSTRACT

A multicore fiber includes: a cladding; and three or more and five or less cores disposed at rotationally asymmetric positions on a circumference centered at a center of the cladding. No core is disposed at the center of the cladding. Angles formed by adjacent ones of lines connecting the center of the cladding and respective ones of the cores are all larger than 60°.

TECHNICAL FIELD

The present invention relates to a multicore fiber, an optical fibercable, and an optical connector.

BACKGROUND

In recent optical fiber communication systems, a large number of opticalfibers such as several tens to several thousands of optical fibers areused, and the amount of transmission information has dramaticallyincreased. In order to reduce the number of optical fibers in suchoptical fiber communication systems, a multicore fiber in which aplurality of cores is arranged in a cladding has been proposed. Forexample, Patent Literature 1 described below describes a multicore fiberin which six outer cores are arranged at equal intervals on thecircumference centered on a center core arranged at a center of acladding.

[Patent Literature 1] JP 2011-193459 A

However, in the multicore fiber of Patent Literature 1 described above,the center core is arranged at the center of the cladding. Since such acenter core is adjacent to all the outer cores, crosstalk tends toconcentrate on the center core. Therefore, there is a demand forsuppressing such crosstalk of the center core.

Meanwhile, in a case where multicore fibers are connected to each other,there is a case where it is desired to specify a desired core from aplurality of cores of one multicore fiber, specify a desired core from aplurality of cores of the other multicore fiber, and connect thespecified desired cores to each other. However, in the multicore fiberof Patent Literature 1 described above, the six outer cores are arrangedat equal intervals, and the outer cores are arranged at rotationallysymmetric positions. Therefore, it is difficult to specify a desiredcore in each of the one and the other multicore fibers and then connectthese multicore fibers to each other unless a marker or the like isused. In addition, there is a case where the marker is smaller than thecore, and in this case, even if there is a marker, it is difficult tospecify a desired core and then connect these multicore fibers to eachother.

SUMMARY

Therefore, one or more embodiments of the present invention provide amulticore fiber, an optical fiber cable, and an optical connectorcapable of suppressing crosstalk and facilitating connection.

A multicore fiber according to one or more embodiments of the presentinvention includes a cladding, and three or more and five or less coresarranged at non-rotationally symmetric positions on a circumferencecentered on the center of the cladding, in which no core is arranged atthe center of the cladding, and angles formed by lines adjacent to eachother among a plurality of lines connecting the center of the claddingand each of the cores arranged on the circumference are all larger than60°.

In this multicore fiber, since no core is arranged at the center of thecladding, unlike Patent Literature 1 described above, crosstalk does notconcentrate on the core arranged at the center of the cladding.Meanwhile, in general, in a multicore fiber, a core tends to be arrangedat a position away from a cover layer to some extent from the viewpointof suppressing absorption of light by the cover layer, the viewpoint ofsuppressing the influence of disturbance or the like from reaching thecore, and the like. In addition, from the viewpoint of suppressingcrosstalk, the core pitch tends to be increased as much as possible.Therefore, when the cladding diameter is the same, the radius of thecircle in a case where the cores are arranged on the circumferencecentered on the center of the cladding tends to be substantially thesame regardless of the number of cores. In the multicore fiber of thepresent invention, since the number of cores arranged on thecircumference described above is three or more and five or less and theangles described above are all larger than 60°, the distance betweenadjacent cores is larger than the distance from the center of thecladding to the core. Therefore, it is possible to suppress crosstalkbetween adjacent cores as compared with the multicore fiber of PatentLiterature 1 described above in which the distance between the adjacentcores is equal to the distance from the center of the cladding to thecore.

Meanwhile, in a case where the cores are arranged rotationallysymmetrically in the multicore fiber, it is difficult to specify adesired core unless a marker or the like is used as described above.However, since the cores are arranged at non-rotationally symmetricpositions in the multicore fiber of the present invention, a desiredcore can be easily specified in each of one and the other multicorefibers without separately providing a marker or the like. Therefore, themulticore fibers can be easily connected to each other.

Here, the non-rotational symmetry refers to the relationship in whichthe arrangement of the cores before rotation and the arrangement of thecores after rotation do not match unless the multicore fiber is rotatedonce about the axis.

In addition, at least two cores of the cores may be arranged atnon-line-symmetric positions with reference to a line passing throughthe center of the cladding and extending along the radial direction ofthe cladding.

When the cores are arranged at non-line-symmetric positions in the abovemanner, the appearance of the plurality of cores at one end of themulticore fiber is different from the appearance of the plurality ofcores at the other end. Therefore, the multicore fibers can be connectedto each other by distinguishing both end portions of the multicorefibers.

In addition, the angles may all be different.

In this case, since the angles formed by the cores are different fromeach other, it is possible to easily specify all the cores.

In addition, when the angles described above are all different, thenumber of cores may be four or more and the cores may be arranged suchthat the narrowest angle and the second narrowest angle are not adjacentto each other.

In this way, it is possible to suppress at least three cores from beingdensely arranged on the circumference described above. Therefore, it ispossible to effectively suppress the crosstalk from concentrating on aspecific core.

In addition, the number of cores may be four or more, two angles of theangles may be different from other angles, the two angles may bedifferent from each other, and all the other angles may be the same.

In this case, since the structure is the simplest among the structuresin which the plurality of cores is arranged at non-line-symmetricpositions, a simple multicore fiber configuration can be realized.

In addition, an optical fiber cable according to one or more embodimentsof the present invention includes a sheath and the multicore fiberaccording to any of the above arranged in the sheath.

With the multicore fiber described above, crosstalk can be suppressedand connection can be facilitated. Therefore, an optical fiber cableincluding such a multicore fiber can suppress crosstalk and facilitateconnection.

In addition, an optical connector according to one or more embodimentsof the present invention includes a ferrule and the multicore fiberaccording to any of the above, and the multicore fiber described aboveis arranged in a fiber insertion hole of the ferrule described above.

With the multicore fiber described above, crosstalk can be suppressedand connection can be facilitated. Therefore, an optical connectorincluding such a multicore fiber can suppress crosstalk and facilitateconnection.

As described above, according to the present invention, a multicorefiber, an optical fiber cable, and an optical connector capable ofsuppressing crosstalk and facilitating connection can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a structure of a cross sectionperpendicular to a longitudinal direction of a conventional opticalfiber.

FIG. 2 is a diagram illustrating a structure of a cross sectionperpendicular to a longitudinal direction of a multicore fiber accordingto first embodiments.

FIG. 3 is a diagram illustrating a structure of a cross sectionperpendicular to a longitudinal direction of a multicore fiber accordingto second embodiments.

FIG. 4 is a diagram illustrating a structure of a cross sectionperpendicular to a longitudinal direction of a multicore fiber accordingto third embodiments.

FIG. 5 is a diagram illustrating a structure of a cross sectionperpendicular to a longitudinal direction of a multicore fiber accordingto fourth embodiments.

FIG. 6 is a diagram illustrating a structure of a cross sectionperpendicular to a longitudinal direction of an example of an opticalfiber cable including the multicore fiber according to the firstembodiments.

FIG. 7 is a plan view illustrating an end side of an example of anoptical connector including the multicore fiber according to the firstembodiments.

FIG. 8 is a front view illustrating a ferrule and a multicore fiber ofthe optical connector illustrated in FIG. 7 .

DETAILED DESCRIPTION

Aspects for carrying out the multicore fiber, the optical fiber cable,and the optical connector according to the present invention will beillustrated below together with the accompanying drawings. Theembodiments illustrated below are for facilitating the understanding ofthe present invention, and are not for limiting the interpretation ofthe present invention. The present invention can be changed or modifiedfrom the embodiments below without departing from the spirit. Inaddition, in the present specification, the dimensions of each membermay be exaggerated for ease of understanding.

Reference Example

First, before describing the embodiments, a reference example will bedescribed. FIG. 1 is a diagram illustrating a structure of a crosssection perpendicular to a longitudinal direction of a multicore fiber100 of the reference example. Note that, in FIG. 1 , hatching is omittedto avoid complication of the drawing.

As illustrated in FIG. 1 , the multicore fiber 100 of the referenceexample includes, as main configurations, a cladding 103, a center core101 arranged at the center of the cladding 103, six outer cores 102A to102F arranged on a circumference Cr centered on the center of thecladding 103, and a cover layer covering the cladding 103. Note that, inFIG. 1 , illustration of the cover layer is omitted to avoidcomplication of the drawing. In the multicore fiber 100, the outer core102B, the outer core 102C, the outer core 102D, the outer core 102E, andthe outer core 102F are arranged in this order clockwise with referenceto one outer core 102A.

The center core 101 and the outer cores 102A to 102F are formed to havethe same diameter and the same refractive index, and propagate light ofa fundamental mode or propagate light of several higher order modes inaddition to the light of the fundamental mode. The refractive index ofeach of the center core 101 and the outer cores 102A to 102F is higherthan the refractive index of the cladding 103. Examples of the materialconstituting the center core 101 and the outer cores 102A to 102Finclude quartz to which an element such as germanium (Ge) for increasingthe refractive index is added. When an element for increasing therefractive index is added to the center core 101 and the outer cores102A to 102F, examples of the material constituting the cladding 103include pure quartz to which no dopant is added and quartz to which anelement such as fluorine (F) for reducing the refractive index is added.In addition, examples of the material constituting the center core 101and the outer cores 102A to 102F include the pure quartz describedabove. When the center core 101 and the outer cores 102A to 102F areformed of pure quartz, examples of the material constituting thecladding 103 include quartz to which an element such as fluorine (F) forreducing the refractive index is added.

In this example, the center core 101 and the two outer cores adjacent toeach other are arranged on an equilateral triangle on the apexes ofwhich the center of each of the three cores is located. Therefore, theangles formed by the lines adjacent to each other among the plurality oflines connecting the center of the center core 101 and the centers ofthe outer cores 102A to 102F are all 60°. Therefore, when a circlehaving a radius that is a line segment connecting the center of thecenter core 101 and the center of each of the outer cores 102A to 102Fis the circumference Cr, a radius CP of the circumference Cr and a corepitch PP corresponding to the length of a line segment connecting thecenters of adjacent outer cores are the same length. Therefore, theouter cores 102A to 102F of this example are arranged at rotationallysymmetric positions on the circumference centered on the center of thecladding 103, and are arranged at line-symmetric positions withreference to a predetermined reference line passing through the centerof the cladding 103. In addition, the core pitch PP is, for example,approximately 25 μm to approximately 50 μm, and crosstalk betweenadjacent outer cores is suppressed to a predetermined reference value orless.

In such multicore fiber 100, the center core 101 is arranged at thecenter of the cladding 103. Since such center core 101 is adjacent toall the outer cores 102A to 102F, crosstalk tends to concentrate on thecenter core 101. In addition, since the arrangement of the outer cores102A to 102F is rotationally symmetric as described above, it isdifficult to distinguish a specific core from the outer cores 102A to102F unless a marker or the like is used. In addition, since thearrangement of the outer cores 102A to 102F is line-symmetric asdescribed above, the appearance of the plurality of cores at one end ofthe multicore fiber 100 is the same as the appearance of the pluralityof cores at the other end. Therefore, it is difficult to distinguish oneend and the other end of the multicore fiber 100.

First Embodiments

Next, the first embodiments will be described. FIG. 2 is a diagramillustrating a structure of a cross section perpendicular to alongitudinal direction of the multicore fiber of the first embodiments.Note that, in FIG. 2 , hatching is omitted to avoid complication of thedrawing.

As illustrated in FIG. 2 , a multicore fiber 10 of one or moreembodiments includes a cladding 13, four cores 12A to 12D arranged on acircumference Cr centered on a center 13A of the cladding 13, and acover layer covering the cladding 13. In addition, no core is arrangedat the center 13A of the cladding 13, and no core is arranged betweenthe center 13A of the cladding 13 and the cores 12A to 12D and outsidethe cores 12A to 12D. Note that, in FIG. 2 , illustration of the coverlayer is omitted to avoid complication of the drawing. In the multicorefiber 10, the core 12B, the core 12C, and the core 12D are arranged inthis order clockwise with reference to one core 12A.

The cladding 13 is formed of the same material as the cladding 103 ofthe reference example, and is formed to have the same diameter and thesame refractive index as those of the cladding 103. In addition, thecores 12A to 12D are formed of the same material as the center core 101and the outer cores 102A to 102F of the reference example, and areformed to have the same core diameter and the same refractive index asthose of the center core 101 and the outer cores 102A to 102F.

Here, assuming that an angle formed by lines adjacent to each otheramong a plurality of lines connecting the center 13A of the cladding 13and the center of each of the cores 12A to 12D is an angle formed by thecores, in one or more embodiments, the angles formed by the cores areall larger than 60°. Of angles θ₁ to θ₄ formed by the plurality ofcores, the angle θ₃ formed by the cores 12C and 12D is 99°. On the otherhand, the angle θ₁ formed by the cores 12A and 12B, the angle θ₂ formedby the cores 12B and 12C, and the angle θ₄ formed by the cores 12D and12A are each 87°. As described above, in one or more embodiments, onlyone angle θ₃ of the angles θ₁ to θ₄ formed by the cores is differentfrom the other angles, and all the other angles θ₁, θ₂, and θ₄ are thesame. Therefore, the cores 12A to 12D are arranged at non-rotationallysymmetric (or rotationally asymmetric) positions on the circumferenceCr. Here, the above-described lines connect the center of the cladding13 and the center of each of the cores 12A to 12D, but the lines do notnecessarily pass through the center of each core. For example, theabove-described lines may connect the center of the cladding 13 and thenon-central portion of each of the cores 12A to 12D.

Next, the relationship between the angle formed by the cores, the radiusCP of the circumference Cr, and the core pitch of one or moreembodiments will be described.

The magnitude relationship between the radius CP of the circumference Crand the core pitch is determined by the angle formed by the cores. Asdescribed above, since the angle θ₁ formed by the cores 12A and 12B is87°, the center 13A of the cladding 13 is located on the apex forming anapex angle of an isosceles triangle in which the angle of the apex angleis 87°, and the centers of the cores 12A and 12B are located on theapexes forming the base angles. The length of each of the two equalsides of this isosceles triangle is the radius CP of the circumferenceCr. Therefore, a core pitch PP1 between the cores 12A and 12B is largerthan the radius CP of the circumference Cr.

As described above, the angles θ₁ to θ₄ formed by the cores are largerthan 60°. Therefore, the core pitch PP2 between the cores 12B and 12C,the core pitch PP3 between the cores 12C and 12D, and the core pitch PP4between the cores 12D and 12A are each larger than the radius CP of thecircumference Cr.

As described above, the multicore fiber 10 of one or more embodimentsincludes the cladding 13, and the four cores 12A to 12D arranged atnon-rotationally symmetric positions on the circumference Cr centered onthe center 13A of the cladding 13, in which no core is arranged at thecenter 13A of the cladding 13, and the angles θ₁ to θ₄ formed by thecores are all larger than 60°.

With such multicore fiber 10 of one or more embodiments, since no coreis arranged at the center 13A of the cladding 13, unlike the referenceexample described above, crosstalk does not concentrate on the corearranged at the center of the cladding. Meanwhile, in general, in amulticore fiber, a core tends to be arranged at a position away from acover layer to some extent from the viewpoint of suppressing absorptionof light by the cover layer, the viewpoint of suppressing the influenceof disturbance or the like from reaching the core, and the like. Inaddition, from the viewpoint of suppressing crosstalk, the core pitchtends to be increased as much as possible. Therefore, when the claddingdiameter is the same, the radius of the circle in a case where the coresare arranged on the circumference centered on the center of the claddingtends to be substantially the same regardless of the number of cores. Inthe multicore fiber 10, since the number of cores arranged on thecircumference Cr is three or more and five or less and the angles θ₁ toθ₄ formed by the cores are all larger than 60°, the core pitch is largerthan the distance from the center of the cladding to the core.Therefore, it is possible to suppress crosstalk between adjacent coresas compared with, for example, the multicore fiber 100 of the referenceexample in which the core pitch is equal to the distance from the centerof the cladding to the core.

In addition, in one or more embodiments, as described above, since thearrangement of the cores 12A to 12D is non-rotationally symmetric, it ispossible to easily specify a desired core from the cores 12A to 12Dwithout separately providing a marker or the like. Therefore, themulticore fibers 10 can be easily connected to each other by makingspecified desired cores correspond to each other.

In addition, in one or more embodiments, the example in which the numberof cores is four has been described, but the number of cores may bethree or five. In such a case, when the angles formed by the cores areall larger than 60°, all the core pitches are larger than the radius CPof the circumference Cr. Therefore, the crosstalk between adjacent corescan be suppressed. In addition, when the number of cores is three orfive, by arranging the cores non-rotationally symmetrically, it ispossible to easily specify a desired core from among a plurality ofcores, and it is possible to easily connect multicore fibers to eachother.

Note that when the number of cores is three in one or more embodiments,for example, the angles formed by the two cores may be 115°, and theangle formed by the remaining one core may be 130°. In addition, theangles formed by the two cores may be 110°, and the angle formed by theremaining one core may be 140°. Alternatively, other angles may be set.

In addition, when the number of cores is five in one or moreembodiments, for example, the angles formed by the four cores may be70°, and the angle formed by the remaining one core may be 80°. Inaddition, the angles formed by the four cores may be 69°, and the angleformed by the remaining one core may be 84°. In addition, the anglesformed by the four cores may be 68°, and the angle formed by theremaining one core may be 88°. Alternatively, other angles may be set.As described above, among the angles formed by the plurality of outercores, only one angle may be different from the other angles, and allthe other angles may be the same. With such a structure, since all theother angles described above are the same, since the structure is thesimplest among the structures that satisfy non-rotational symmetry, asimple multicore fiber configuration can be realized.

Second Embodiments

Next, the second embodiments will be described. FIG. 3 is a diagramillustrating a structure of a cross section perpendicular to alongitudinal direction of the multicore fiber of the second embodiments.Note that the same or equivalent components as those of the firstembodiments are designated by the same reference numerals and duplicateddescription will be omitted unless otherwise specified. In addition, inFIG. 3 , hatching is omitted and illustration of a cover layer isomitted to avoid complication of the drawing.

As illustrated in FIG. 3 , the configuration of a multicore fiber 20 ofone or more embodiments is the same as the configuration of themulticore fiber 10 except that the arrangement of cores 12A to 12D on acircumference Cr is different from that of the multicore fiber 10 of thefirst embodiments.

In one or more embodiments, the angles formed by the cores are alllarger than 60°. Among angles 74 1 to θ₄ formed by the plurality ofcores, the angles θ₁ and θ₂ are 85°, the angle θ₃ is 91°, and the angleθ₄ is 99°. As described above, in one or more embodiments, only twoangles θ₃ and θ₄ of the angles θ₁ to θ₄ formed by the cores aredifferent from the other angles θ₁ and θ₂, and the other angles θ₁ andθ₂ are the same. In addition, these two angles θ₃ and θ₄ are differentfrom each other. With the configuration illustrated in FIG. 3 , thecores 12A to 12D are arranged at non-rotationally symmetric positionsand are arranged at non-line-symmetric (or line-asymmetric) positionsbased on a line passing through the center of the circumference Cr orthe cladding and extending along the radial direction of the cladding.Here, the number of cores arranged at non-line-symmetric positions basedon the line passing through the center of the circumference Cr or thecladding and extending along the radial direction of the cladding is notlimited to the above-described number of cores, and it is sufficient ifat least two cores are arranged.

Thus, in one or more embodiments, since the cores 12A to 12D arearranged at non-rotationally symmetric positions, it is possible toeasily specify a desired core from the cores 12A to 12D. Therefore, themulticore fibers 20 can be easily connected to each other by makingspecified desired cores correspond to each other. In addition, when thecores 12A to 12D are arranged at the non-line-symmetric positions asillustrated in FIG. 3 , the appearance of the plurality of cores at oneend of the multicore fiber 20 is different from the appearance of theplurality of cores at the other end. Therefore, the multicore fibers 20can be connected to each other by distinguishing one end and the otherend of the multicore fibers 20.

Meanwhile, as described above, the angles θ₁ to θ₄ formed by the coresare larger than 60°. Therefore, the core pitches PP1 to PP4 in one ormore embodiments are larger than the radius CP of the circumference Cr.Therefore, the crosstalk of the adjacent cores can be suppressed ascompared with the case where the radius CP is the same size as the corepitches PP1 to PP4.

In this case, since the structure is the simplest among the structuresin which the plurality of cores is arranged at non-line-symmetricpositions, a simple multicore fiber configuration can be realized.

In addition, in one or more embodiments, the number of cores may be fiveas in the first embodiments. Even in this case, as described in thefirst embodiments, the core pitch is larger than the radius CP of thecircumference Cr. Therefore, the crosstalk between adjacent cores can besuppressed. In addition, by arranging the five cores non-rotationallysymmetrically, it is possible to easily specify a desired core fromamong a plurality of cores and it is possible to easily connectmulticore fibers to each other as described above.

Note that when the number of cores is five in one or more embodiments,for example, the angles formed by the three cores may be 68°, one of theangles formed by the remaining two cores may be 74°, and the other anglemay be 82°. Alternatively, other angles may be set.

Third Embodiments

Next, the third embodiments will be described. FIG. 4 is a diagramillustrating a structure of a cross section perpendicular to alongitudinal direction of the multicore fiber of the third embodiments.Note that the same or equivalent components as those of the firstembodiments are designated by the same reference numerals and duplicateddescription will be omitted unless otherwise specified. In addition, inFIG. 4 , hatching is omitted and illustration of a cover layer isomitted to avoid complication of the drawing.

As illustrated in FIG. 4 , the configuration of a multicore fiber 30 ofone or more embodiments is the same as the configuration of themulticore fiber 10 except that the arrangement of cores 12A to 12D on acircumference Cr is different from that of the multicore fiber 10 of thefirst embodiments and that of the multicore fiber 20 of the secondembodiments.

In one or more embodiments, the angles formed by the cores are alllarger than 60°. Of angles θ₁ to θ₄ formed by the cores, the angle θ₁ is85°, which is the narrowest angle, the angle θ₂ is 88°, which is thesecond narrowest angle, the angle θ₃ is 92°, and the angle θ₄ is 95°. Asdescribed above, in one or more embodiments, the angles θ₁ to θ₄ are alldifferent. In addition, among the angles θ₁ to θ₄, the narrowest angleθ₁ and the second narrowest angle θ₂ are adjacent to each other. Withsuch a configuration, the cores 12A to 12D are arranged atnon-rotationally symmetric positions and are arranged atnon-line-symmetric positions based on a line passing through the centerof the circumference Cr.

As described above, in one or more embodiments, since the angles θ₁ toθ₄ formed by the cores are all different, each of the cores 12A to 12Dcan be specified. Therefore, it is possible to easily connect themulticore fibers 30 in such a manner that each of the cores 12A to 12Dof one multicore fiber 30 corresponds to each of the cores 12A to 12D ofthe other multicore fiber 30. In addition, since the arrangement of thecores 12A to 12D is non-line-symmetric, the appearance of the pluralityof cores at one end of the multicore fiber 30 is different from theappearance of the plurality of cores at the other end. Therefore, themulticore fibers 30 can be connected to each other by distinguishing oneend and the other end of the multicore fibers 30.

In addition, in one or more embodiments, the number of cores may bethree or five. Even in this case, as described in the first embodiments,the core pitch is larger than the radius CP of the circumference Cr.Therefore, the crosstalk between adjacent cores can be suppressed. Inaddition, by arranging the three or five cores non-rotationallysymmetrically, it is possible to easily specify a desired core fromamong a plurality of cores and it is possible to easily connectmulticore fibers to each other as described above. In addition, when theangles formed by the cores are all different, the arrangement of thecores is non-line-symmetric as described above. Therefore, since theappearance of the plurality of cores at one end of the multicore fiberis different from the appearance of the plurality of cores at the otherend, the multicore fibers can be connected by distinguishing one end andthe other end of the multicore fibers.

Note that when the number of cores is three in one or more embodiments,the angles formed by the cores may, for example, be 115°, 120°, and 125°or may be 110°, 120°, and 130° clockwise. Alternatively, other anglesmay be set. In addition, when the number of cores is five in one or moreembodiments, for example, the angles formed by the cores may be 66°,69°, 72°, 75°, and 78° clockwise. Alternatively, other angles may beset.

Fourth Embodiments

Next, the fourth embodiments will be described. FIG. 5 is a diagramillustrating a structure of a cross section perpendicular to alongitudinal direction of the multicore fiber of the fourth embodiments.Note that the same or equivalent components as those of the firstembodiments are designated by the same reference numerals and duplicateddescription will be omitted unless otherwise specified. In addition, inFIG. 5 , hatching is omitted and illustration of a cover layer isomitted to avoid complication of the drawing.

As illustrated in FIG. 5 , the configuration of a multicore fiber 40 ofone or more embodiments is the same as the configuration of themulticore fiber 10 except that the arrangement of cores 12A to 12D on acircumference Cr is different from that of the multicore fiber 10 of thefirst embodiments, that of the multicore fiber 20 of the secondembodiments, and that of the multicore fiber 30 of the thirdembodiments.

The multicore fiber 40 of one or more embodiments is similar to themulticore fiber 30 of the third embodiments in that the angles formed bythe cores are all different, but the arrangement of the cores 12A to 12Dis different from the arrangement of the cores 12A to 12D in themulticore fiber 30. In one or more embodiments, the angle θ₁ is 85°,which is the narrowest angle, the angle θ₂ is 92°, the angle θ₃ is 88°,which is the second narrowest angle, and the angle θ₄ is 95°. Asdescribed above, in one or more embodiments, the cores 12A to 12D arearranged such that the narrowest angle 85° and the second narrowestangle 88° are not adjacent to each other.

With such a configuration, the same effects as those of the thirdembodiments can be obtained.

In addition, in one or more embodiments, as described above, since thecores 12A to 12D are arranged such that the narrowest angle formed bythe cores and the second narrowest angle formed by the cores are notadjacent to each other, it is possible to suppress at least three coresfrom being densely arranged on the circumference Cr. Therefore, it ispossible to effectively suppress the crosstalk from concentrating on aspecific core among the cores 12A to 12D.

In addition, in one or more embodiments, the number of cores may befive. In this case, for example, the angles formed by the cores may be66°, 75°, 72°, 69°, and 78° clockwise. With such an angle pattern, thenarrowest angle 66° formed by the cores and the second narrowest angle69° formed by the cores are not adjacent to each other. Note that thecores may be arranged in another angle pattern such that the narrowestangle formed by the cores and the second narrowest angle formed by thecores are not adjacent to each other.

The multicore fiber of the present invention has been described bytaking the first to fourth embodiments as an example, but the presentinvention is not limited thereto. The configuration of the multicorefiber can be changed as long as the multicore fiber includes a cladding,and three or more and five or less cores arranged at non-rotationallysymmetric positions on a circumference centered on the center of thecladding described above, in which no core is arranged at the center ofthe cladding described above, angles formed by lines adjacent to eachother among a plurality of lines connecting the center of the claddingdescribed above and the center of each of the cores described above areall larger than 60°.

For example, the multicore fiber may be formed in a trench shape.

In addition, the refractive indices and diameters of the cores adjacentto each other may be different from each other.

In addition, the angles formed by the cores described in the aboveembodiments are an example, and the angles formed by the cores can beappropriately changed.

Next, an example of an optical fiber cable including the multicore fiberof the present invention will be described.

FIG. 6 is a diagram illustrating a structure of a cross sectionperpendicular to a longitudinal direction of an optical fiber cable 1including the multicore fiber 10 of the first embodiments. Asillustrated in FIG. 6 , the optical fiber cable 1 includes a sheath 4and the multicore fiber 10 according to the first embodiments arrangedin the sheath 4. The multicore fiber 10 includes the cores 12A to 12D,the cladding 13, and the cover 14 covering the cladding 13. Note that,in FIG. 6 , illustration of the cores 12A to 12D is omitted to avoidcomplication of the drawing.

The shape of the sheath 4 is a cylindrical shape in a cross sectionperpendicular to the longitudinal direction, and a central portion inthe cross section is a circular cavity. The sheath 4 includes a sheathbody portion 41 and a reinforcing member 42. The sheath body portion 41is made of resin and forms an outer shape of the sheath 4. Examples ofthe resin constituting the sheath body portion 41 include thermoplasticresin. Examples of the thermoplastic resin include resins such aspolyvinyl chloride (PVC), polyethylene (PE), polyamide (PA), ethylenefluoride, and polypropylene (PP). The reinforcing member 42 is a memberincluding, for example, a wire and giving strength to the optical fibercable 1. The reinforcing member 42 is made of, for example, copper,iron, nickel, stainless steel, fiber reinforced plastic (FRP), or thelike.

As described above, the optical fiber cable 1 includes the multicorefiber 10 in which crosstalk can be suppressed. Therefore, the crosstalkof the optical fiber cable can be suppressed. In addition, when theoptical fiber cables 1 are connected to each other, as described above,a desired core (for example, core 12A) of each multicore fiber 10included in one optical fiber cable 1 can be specified, and a core (forexample, core 12A) corresponding to the desired core of the onemulticore fiber in each multicore fiber 10 included in the other opticalfiber cable 1 can be specified. Therefore, the optical fiber cables 1can be easily connected to each other by making desired cores correspondto each other.

Note that an optical fiber cable may be configured using at least one ofthe multicore fiber 20 of the second embodiments, the multicore fiber 30of the third embodiments, and the multicore fiber 40 of the fourthembodiments instead of the multicore fiber 10 of the first embodimentsor together with the multicore fiber 10.

In addition, the optical fiber cable 1 described above is an example,and may be an optical fiber cable having another configuration.

Next, an example of an optical connector including the multicore fiberof the present invention will be described.

FIG. 7 is a plan view illustrating an end side of an optical connector 2including the multicore fiber 10 according to the first embodiments. Theoptical connector 2 is, for example, a multifiber push-on (MPO) opticalconnector. As illustrated in FIG. 7 , the optical connector 2 includesat least one multicore fiber 10 and a ferrule 50. The ferrule 50 is amember that holds the end portion of the multicore fiber 10, and isformed of, for example, resin. In addition, the multicore fiber 10 isarranged in a fiber insertion hole of the ferrule 50.

FIG. 8 is a front view illustrating the ferrule 50 and the multicorefiber 10 of the optical connector 2 illustrated in FIG. 7 . Asillustrated in FIG. 8 , a pair of guide pin insertion holes 52 and aplurality of fiber insertion holes 51 are formed in the ferrule 50.Guide pins, which are not illustrated, are inserted into the guide pininsertion holes 52, and the optical connector 2 on one side and theoptical connector 2 on the other side are connected via the guide pins.The end portions of the multicore fiber 10 are inserted into the fiberinsertion holes 51, and the end portions of the multicore fiber 10protrude from an end surface 50A of the ferrule 50. Note that a portionof the multicore fiber 10 protruding from the end surface 50A may be cutout, and the end surface of the multicore fiber 10 and the end surface50A of the ferrule 50 may be flush with each other.

As described above, the optical connector 2 includes the multicore fiber10 in which crosstalk can be suppressed. Therefore, the crosstalk of theoptical connector 2 can be suppressed. In addition, when the opticalconnectors 2 are connected to each other, as described above, a desiredcore of each multicore fiber 10 included in one optical connector 2 canbe specified, and a core corresponding to the desired core of the onemulticore fiber in each multicore fiber 10 included in the other opticalconnector 2 can be specified. Therefore, the optical connectors 2 can beeasily connected to each other by making desired cores correspond toeach other. In addition, in this case, a desired outer core of theplurality of multicore fibers included in the optical connector 2 can bespecified, and it is easy to align the core arrangement of the pluralityof multicore fibers in the same manner in the connector cross section.

Note that an optical connector may be configured using at least one ofthe multicore fiber 20 of the second embodiments, the multicore fiber 30of the third embodiments, and the multicore fiber 40 of the fourthembodiments instead of the multicore fiber 10 of the first embodimentsor together with the multicore fiber 10.

In addition, the optical connector 2 described above is an example, andmay be an optical connector having another configuration.

According to the present invention, a multicore fiber, an optical fibercable, and an optical connector capable of suppressing crosstalk andfacilitating connection can be provided, and can be used, for example,in the field of communication or the like.

Although the disclosure has been described with respect to only alimited number of embodiments, those skilled in the art, having benefitof this disclosure, will appreciate that various other embodiments maybe devised without departing from the scope of the present invention.Accordingly, the scope of the invention should be limited only by theattached claims.

1. A multicore fiber comprising: a cladding; and three or more and fiveor less cores disposed at rotationally asymmetric positions on acircumference centered at a center of the cladding, wherein no core isdisposed at the center of the cladding, and angles formed by adjacentones of lines connecting the center of the cladding and respective onesof the cores are all larger than 60°.
 2. The multicore fiber accordingto claim 1, wherein two or more of the cores are disposed at linearlyasymmetric positions with reference to a line passing through the centerof the cladding and extending along a radial direction of the cladding.3. The multicore fiber according to claim 1, wherein the angles are alldifferent.
 4. The multicore fiber according to claim 3, wherein a numberof cores is four or more, and a narrowest angle of the angles is notadjacent to a second narrowest angle of the angles.
 5. The multicorefiber according to claim 1, wherein a number of cores is four or more,two angles of the angles are different from remaining angles, the twoangles are different from each other, and all of the remaining anglesare same.
 6. An optical fiber cable comprising: a sheath; and themulticore fiber according to claim 1 in the sheath.
 7. An opticalconnector comprising: a ferrule; and the multicore fiber according toclaim 1, wherein one end of the multicore fiber is disposed in a fiberinsertion hole of the ferrule.